reverse-int-javascript

Introduction

This is the 3rd post in the series DS and Algo Practice - using examples and snippets.

We would leverage our previous string reversal techniques to reverse and return back an integer.

Problem Statement

Reverse an integer, preserve the negative sign if it exists, remove the facing zeros, if they exist.

For ex: 3000 would be reversed to 3 -> facing zeros need to be removed.

-90091 would be reversed to -19009 -> negative sign needs to be persisted.

Implementations

1) A crude implementation

Input Integer -> Convert to String Array -> Search for negative sign -> Reverse the string -> Append the negative sign if the search yields true -> Convert the reversed string back to the integer.

function reverseInt(number) {
  if (!number || isNaN(number)) {
    return "Invalid format - input is not a integer";
  }
  let strArray = number.toString().split("");
  let isNegative = strArray.indexOf("-") !== -1 ? true : false;
  let reversedStr = strArray.reverse().join("");
  reversedStr = isNegative ? `${"-"}${reversedStr}` : reversedStr;
  return parseInt(reversedStr);
}

console.log(reverseInt(123));
console.log(reverseInt(-981));
console.log(reverseInt(500));
console.log(reverseInt(-900));
console.log(reverseInt(-900123));
console.log(reverseInt(""));
console.log(reverseInt("hello world"));
console.log(reverseInt(null));
console.log(reverseInt(NaN));

2) Using Math.sign(num) method.

Math.sign(num) method returns +1/-1 depending upon the passed in number.

This method simplifies the above implementation.

Input Integer -> Convert to String Array and Reverse it -> Parse the reversed string back to Integer -> Multiply the reversed integer with Math.sign(Input Integer)

//Alternate approach using Math.sign() method
function reverseIntAlternate(number) {
  if (!number || isNaN(number)) {
    return "Invalid format - input is not a integer";
  }

  let reversedNumber = parseInt(number.toString().split("").reverse().join(""));

  return reversedNumber * Math.sign(number);
}

console.log(reverseIntAlternate(123));
console.log(reverseIntAlternate(-981));
console.log(reverseIntAlternate(500));
console.log(reverseIntAlternate(-900));
console.log(reverseIntAlternate(-900123));
console.log(reverseIntAlternate(""));
console.log(reverseIntAlternate("hello world"));
console.log(reverseIntAlternate(null));
console.log(reverseIntAlternate(NaN));

Github link

Code is available at - https://github.com/anurag1302/dsalgo-javascript/blob/main/practice/reverse-int/index.js

Reverse an Integer - via JavaScript

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React Js – Getting Started

Introduction

Problem Statement

Implementations

1) A crude implementation

2) Using Math.sign(num) method.

Github link

Command Palette

Comments

Data Structures & Algorithms Practice - via examples and snippets

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More from this blog

Introduction

Problem Statement

Implementations

1) A crude implementation

2) Using Math.sign(num) method.

Github link